Improve admin UI visual design — polish look and feel (#59)

* Improve admin UI visual design — polish look and feel

- Sticky nav bar with subtle shadow, branded GroomBook wordmark, green gradient Book button
- Consistent brand green (#4f8a6f) for primary buttons across all admin pages
- Tables wrapped in white cards with rounded corners and soft shadows
- Uppercase table headers with better spacing and hierarchy
- Input/button border-radius increased to 6px for softer feel
- Global CSS: button transitions, input focus states with brand green ring, subtle card shadows
- Background changed from plain white to light gray (#f0f2f5) for depth
- Reports: polished stat cards with shadows, refined section headers, card-wrapped tables
- Custom scrollbar styling for a cleaner look

Closes groombook/groombook#58

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* Fix test selectors for branded nav text

- Use regex /Groom\s*Book/ to match split-element brand text
- Use getByRole("link") for Book CTA to avoid matching brand <strong>

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* Fix brand text test to handle split-element rendering

The nav brand was changed to <span>Groom</span>Book for color styling,
but getByText with a regex can't match text split across child elements.
Use a custom text matcher that checks the STRONG element's textContent.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* Fix E2E tests for split-element brand name

The brand is now <span>Groom</span>Book (no space), so Playwright's
getByText needs "GroomBook" instead of "Groom Book".

Co-Authored-By: Paperclip <noreply@paperclip.ing>

---------

Co-authored-by: Groom Book CTO <cto@groombook.dev>
Co-authored-by: Paperclip <noreply@paperclip.ing>
Co-authored-by: Groom Book CTO <cto@groombook.app>

apps/web/src/pages/GroupBooking.tsx

@@ -287,7 +287,7 @@ function NewGroupBookingForm({
           <button
             type="submit"
             disabled={saving}
-            style={{ ...btnStyle, backgroundColor: "#3b82f6", color: "#fff", borderColor: "#3b82f6" }}
+            style={{ ...btnStyle, backgroundColor: "#4f8a6f", color: "#fff", borderColor: "#4f8a6f" }}
           >
             {saving ? "Booking…" : "Create Group Booking"}
           </button>
@@ -471,7 +471,7 @@ export function GroupBookingPage() {
         </select>
         <button
           onClick={() => setShowCreate(true)}
-          style={{ ...btnStyle, marginLeft: "auto", backgroundColor: "#3b82f6", color: "#fff", borderColor: "#3b82f6" }}
+          style={{ ...btnStyle, marginLeft: "auto", backgroundColor: "#4f8a6f", color: "#fff", borderColor: "#4f8a6f" }}
         >
           + New Group Booking
         </button>
@@ -558,25 +558,26 @@ function Field({
 }
 
 const btnStyle: React.CSSProperties = {
-  padding: "0.35rem 0.75rem",
+  padding: "0.4rem 0.85rem",
   border: "1px solid #d1d5db",
-  borderRadius: 4,
-  background: "#f9fafb",
+  borderRadius: 6,
+  background: "#fff",
   cursor: "pointer",
   fontSize: 13,
+  fontWeight: 500,
 };
 
 const inputStyle: React.CSSProperties = {
   width: "100%",
-  padding: "0.4rem 0.5rem",
+  padding: "0.45rem 0.6rem",
   border: "1px solid #d1d5db",
-  borderRadius: 4,
+  borderRadius: 6,
   fontSize: 13,
   boxSizing: "border-box",
 };
 
 const tdStyle: React.CSSProperties = {
-  padding: "0.45rem 1rem",
-  borderBottom: "1px solid #f1f5f9",
+  padding: "0.5rem 1rem",
+  borderBottom: "1px solid #f3f4f6",
   color: "#374151",
 };